This application claims the priority of German application 197 56 015.6, filed in Germany on Dec. 17, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for hydraulic rotational angle adjustment of a shaft relative to a drive wheel, especially the camshaft of an internal combustion engine comprising an inner part that is nonrotatably connected with the camshaft, said inner part having at least approximately radially extending ribs or vanes, and a driven compartmented wheel that has a plurality of compartments distributed around the circumference which are subdivided by the ribs or vanes guided in an angularly movable fashion, into two pressure chambers each, for whose pressurization the inner part is rotated relative to the compartmented wheel, and with means for securing the rotational position of the inner part relative to the compartmented wheel.
A device of this kind is known for example from U.S. Pat. No. 4,858,572. In this device according to the species, an internal part is connected nonrotatably with the end of the camshaft, which has a plurality of radial slots distributed around the circumference on its exterior, in which slots vane elements are guided radially displaceably. This interior part is surrounded by a compartmented wheel that has a plurality of hydraulically loadable compartments divided by the vanes into two pressure chambers opposite one another and acting on these compartments. As a result of the pressurization of these pressure chambers, and as a function of the pressure differential, the compartmented wheel can be rotated relative to the inner part and hence relative to the camshaft. In addition, two hydraulically pressurizable pistons are guided in the compartmented wheel, each in a radial bore a in specified angular position, each piston being capable of being inserted into a radial depression of the inner part in the associated end position of the device. These pistons are urged in the direction of the inner part by compression spring elements and are displaceable in the inner ring in the opposite direction by hydraulic pressurization of the bores. The device is intended to be locked in one of its two end positions by these spring-loaded pistons, provided the pressure for pressurizing the pressure chambers does not reach a certain level. It is only when a certain pressure level is reached that the pistons are pushed back against the action of the compression springs and allow the inner part to turn relative to the compartmented wheel. With such a device, it is intended among other things to avoid rattling noises when starting the internal combustion engine, said noises being caused by changing torque loads when starting and operating the engine.
In addition, the device is to be held in a specific rotational position until the pressure level has reached a value that is sufficient to achieve a reliable holding and adjusting effect. However it is disadvantageous that with such a device, locking is only possible in the end positions of the respective adjustment ranges of the device. Moreover, such an arrangement is costly to manufacture because of the radial bores and requires relatively large rib widths in the compartmented wheel to accept the bores and the piston, thus reducing the width of the compartments and sharply limiting the adjustment range of the device.
A device for hydraulic rotational angle adjustment of a camshaft relative to its drive wheel is known from DE 39 37 644 A1, in which a plurality of radially-extending ribs is permanently attached to an inner part nonrotatably connectable with the camshaft, said ribs being rotationally movably mounted in the compartments of a surrounding compartmented wheel and dividing these compartments into two pressure chambers each. However, means for securing the rotational position of the shaft relative to the compartmented wheel are not provided here.
On the other hand, a goal of the invention is to improve a device for hydraulic rotational angle adjustment of a shaft relative to a drive wheel in such fashion that in every rotational position, a secure fastening of the inner part and/or the shaft relative to the compartmented wheel is made possible, thus reliably preventing unwanted changes in position during operation.
This goal is achieved according to the invention by providing a device wherein the means for securing the rotational position constitutes an annular piston that cooperates with at least one axial end face of the ribs or vanes or of the compartmented wheel.
Because the means for securing the rotational position comprise a hydraulically pressurizable annular piston that abuts a common axial end face of the ribs or vanes of the inner part and of the compartmented wheel, locking and/or clamping is possible in every angular position of the two elements relative to one another. As a result, not only can any desired angular positions of the two structural elements relative to one another be secured, but it is also readily possible, especially when used in the valve drive of an internal combustion engine, to avoid rattling noises when starting the engine which are caused in one of the two end positions of the device by exposure to fluctuating torque. As a result, a clamping action that replaces or supports the hydraulic clamping action can be achieved in all rotational positions and permits operation with greater regulating accuracy.
The device according to the invention also has the advantage of being especially simple in construction and thus can be manufactured economically. Assembly is made much simpler, faster, and hence more inexpensive by eliminating the relatively small pistons and spring elements that are costly to install. Moreover, no additional bores in the ribs of the compartmented wheel are necessary, so that the ribs can be made relatively narrow, hence making possible a greater compartment width and/or a greater compartment angle, and consequently a greater adjustment range of the device, with the same number of compartments.
The annular piston of the device can be made economically as an annular disk.
A device of this kind can be built especially simply and economically if the annular piston is arranged relative to the inner part for securing and/or clamping the compartmented wheel in such fashion that it simultaneously serves as the end seal for the pressure chambers.
The annular piston can be guided and secured in a manner that is favorable for manufacturing techniques by a lid element connected with the compartmented wheel on the side facing away from the pressure chambers.
A reliable locking and/or clamping of the two structural elements that are movable relative to one another, which in particular prevents a change in the rotational position for as long as a sufficient pressure level is not reached in the pressure chambers, is obtained when the annular piston under the influence of a spring element reaches a clamping position against the compartmented wheel and the ribs or vanes of the inner part.
The annular piston and the corresponding piston surfaces are designed in an advantageous manner so that when a pressure level is applied in the pressure chambers that is sufficient for relative displacement of the two structural elements with respect to one another, the clamping action of the annular piston is terminated.